Production of cast iron



Patented May 8, 1951 PRODUCTION OF CAST IRON Henton Morrogh, Alvechurch,Birmingham, England, assignor to The British Cast Iron ResearchAssociation, Alvechurch, Birmingham,

England No Drawing. Application October 25, 1949, Se-

rial No. 123,537. In Great Britain October 30,

11 Claims.

This invention relates to the production of cast iron, and moreparticularly to methods for the introduction of magnesium into castiron.

Owing to its volatility and inflammability it is wasteful and dangerousto attempt to add magnesium metal to molten iron, and when it is desiredto introduce-magnesium into cast iron it has been proposed to alloy themagnesium first with a metal such as nickel so as to minimize the lossof magnesium and to limit the risk of fire.

We have found that under certain conditions magnesium may be introducedinto cast iron by the use of a reducible magnesium compound such asmagnesia or a compound convertible into magnesia by the action of heat;such compounds are for example magnesium carbonate, including magnesite,dolomite and chrom-magnesite, or organic magnesium salts such asmagnesium oxalate. We havefound that when molten iron at temperaturesabove 1650 C. is brought into contact with magnesia (or compoundsgenerating magnesia at such temperatures) reduction of the oxide takesplace and magnesium metal becomes available for the desulphurisation ofthe iron and, when the sulphur is or falls below 0.02 per cent, forsolution in the iron.

It is known that silicon and ferrosilicon are able to reduce magnesiumoxide at temperatures above 1100 C. to metallic magnesium. We have foundthat this reaction can be brought about by placing a mixture of magnesia(or magnesiagenerating compounds) and silicon or ferrosilicon in contactwith molten iron above 1100 C., and the magnesium produced is, as above,available for desulphurising and dissolving in the iron.

It is an object of the present invention to provide a method forintroducing magnesium into cast iron. Another object is to provide amethod for the desulphurisation of cast iron by means of magnesium. Afurther object is to provide a method for the production of grey castiron in which the free carbon is present as graphite predominantly inthe form of nodules. A still further object is to provide a method forthe production of alloys of iron and magnesium. Other objects willappear from the following description.

These objects are achieved by the present invention according to whichmagnesium is introduced into cast iron by bringing the molten iron intocontact with magnesia or a magnesia-generating compound at temperaturesabove 1650 C., or with a mixture of magnesia (or a magnesiageneratingcompound) and silicon or ferrosilicon at temperatures above 1100 C. Ifthe iron originally contains more then 0.02 per cent by weight ofsulphur the excess sulphur is first removed by the magnesium, and unlessdesulphurisation is the sole aim, sufficient magnesia or magnesiamixture must be employed to deal with this sulphur and to enter intosolution in the iron.

The reduction by silicon or ferrosilicon occurs more readily in thepresence of small proportions of halides, such as magnesium chloride,calcium fluoride, or magnesium fluoride.

A convenient method of introducing the magnesium is to form a mixture ofmagnesia or burnt dolomite with a ferrosilicon containing, for example,60-99% by Weight of silicon, into briquettes with a suitable bindingagent such as sodium silicate, bentonite or, preferably, Sorel cement.The briquetted bonded mixture may be plunged beneath the surface of themolten iron above 1100 C. in the ladle, and held there until sufficientmagnesium has dissolved in the iron.

The briquettes should contain magnesia, lime and silicon (or theequivalent amount of ferrosilicon) in approximately the proportionsindicated by the equation:

i. e. parts by weight of magnesia, 112 parts of lime and 28 parts ofsilicon. Dolomite burnt at 950 1000 C. provides a mixture of magnesiaand lime in the proportion 45:55, which is sufiiciently near thestoichiometric proportion for the purpose. The ingredients are ground topass at least -80 mesh and well mixed. If bentonite is to be used asbinder, 5% of water is added to the finely powdered mixture and thewhole is ground up with 5% of bentonite, briquetted and allowed to set,and finally dried at 200 C.

The addition of 5% of calcium fluoride to the finely powdered mixtureimproves its activity.

Alternatively, to the finely powdered mixture may be added 5% of waterand 5% of magnesium chloride, which acts both as a binder and anaccelerator. A similar result may be obtained by treating the finelypowdered mixture with up to 5% by weight of a 20% aqueous hydrochloricacid solution, whereby part of the oxides is converted into chlorides.

The invention thus provides a new and practicable method of introducingmagnesium into molten iron by the use of magnesia or amagnesia-generating compound.

In the absence of elementary silicon temperatures above 1650 C. arenecessary; but if the magnesia is associated with silicon, reduction tomagnesium metal takes place at 1100 C. and proceeds more readily at 1250or higher. The

magnesia, with or without silicon, may be applied as a refractory liningto the walls of the furnace or the runs, or the ladle, always bearing inmind that unless the magnesia is associated with a due proportion ofsilicon temperatures above 1650 C. must be used. More conveniently themagnesia-silicon mixture is briquetted as described and held under thesurface of the molten iron in the ladle, at temperatures of 1100" orhigher, until suflicient has dissolved.

Magnesium is a well-known desulphurising agent, and the presentinvention provides a convenient method of reducing the sulphur contentof iron during casting.

When magnesium has been used in quantity more than sufiicient to reducethe sulphur content of the cast iron to below 0.02%, magnesium metaldissolves in the iron, and an alloy containing as much as 1 of magnesiumcan be produced in this way.

If the iron contains sufiicient carbon, or additional carbon isprovided, so that after casting a grey cast iron 'hypereutectic inrespect of carbon results, the graphite in the cast iron wilLwhe'n themagnesium added is more than sufficient to reduce the sulphur content tobelow 0.02 per cent, be predominantly in the nodular form and the castiron will have the greatly improved properties described in my PatentNo. 2,488,511. As in the process of that patent it is advantageous,after the introduction of the nodulising agent (in this case magnesium)to add a graphitising agent, e. g. ferrosilicon, calcium s'ilicide, orgraphite.

I claim:

1. A process for the introduction of magnesium metal into cast ironwhich comprises bringing the molten iron into contact with magnesia attemperatures at which reduction of the magnesia to magnesium takesplace.

2. A-processas claimed in claim 1 in which the magnesia is produced insitu by decomposition of a magnesia-generating compound.

3. A process for the introduction of magnesium metal into cast ironwhich comprises bringing the molten iron at temperatures above 1100 C.into contact with magnesia and silicon.

4. A process as claimed in claim 3 in which the magnesia is produced insitu by decomposition of a'ma'gnesia-generatin'g compound.

5. A process for the introduction'of magnesium metal into cast ironwhich comprises bringing the molten iron at temperatures above 1100 "C.into contact with a briquette compoun'ded'from .a magnesia-providingcompound, selected from the group consisting of magnesia, magnesiumcarbonate, dolomite, chrome-magnesite and organic salts of magnesium,and a silicon-providing-compound selected from the group consisting ofsilicon and ferrosilicon, the briquette being held below the surface ofthe molten iron in the ladle until suflicient magnesium has dissolved.

6. Aprocess as claimed in-claim 5 in which the riquette contains, inaddition to the magnesiaproviding compound and the silicon-providingcompound, an accelerator selected from the group consisting of calciumfluoride and magnesium chloride.

7. A process for the desulphurisation of cast iron which comprisesbringing the molten iron at temperatures above 1100 0. into contact withmagnesia and silicon, these ingredients being applied in such quantityas to provide enough magnesium metal to combine with the amount ofsulphur to be removed.

8. A process for the production of a grey cast iron in which the freecarbon content is at least predominantly in the form of nodular graphitewhich comprises treating a suitable molten iron at temperatures above1100 C. with magnesia and silicon in such quantity as to provide morethan sufficient magnesium metal to reduce the sulphur content of theiron to 0.02%, a suitable molten iron for this purpose being one whichon casting yields a grey cast iron hypereutectic in 'relati'o'ntocarbon.

9. A process as claimed in claim '8 which includes the further step ofadding to the molten iron, after the introduction of the magnesium, agraphitising agent selected from the group cons'isting of ferrosilicon,calcium .silicide and graphite.

:10. A briquetted composition, suitable for the introduction ofmagnesium into cast iron, containing magnesia, calcium oxide and :a:siliconproviding substance, the magnesia and thesil'icon being .present-substantially stoichiometric proportions, together with a magnesiumchloride cement which acts as a binding and accelerating agent.

11. A briquetted composition as claimed in claim 10 in which saidmagnesium chloride icement is Sor'el cement.

FI-IENTON MORROG'H.

REFERENCES CITED The following references are of record in "the file "ofthis patent:

UNITED STATES PATENTS Number Name :Date

1,119,643 Saklatwalla Dec. 1.1911 4 1,239,178 Grosvenor Sept. A, 1191-?2,103,976 Suchy'et al. ?Dec. 28, 1937 2,282,241 Peake .May 5, 119.422,485,760 Millis et al. Oct. '25, I949

3. A PROCESS FOR THE INTRODUCTION OF MAGNESIUM METAL INTO CAST IRONWHICH COMPRISES BRINGING THE MOLTEN IRON AT TEMPERATURES ABOVE 1100* C.INTO CONTACT WITH MAGNESIA AND SILICON.